variation at any one island was large. Range in values in d/m/g dry weight at three islands at Rongelap Atoll was as follows: Eniaetok 369-498, and Rongelap 199-330. Kabelle 324-731, However, the average cesium-137 levels were highest at Kabelle Island, which lies in the northern part of the atoll, and lowest at Rongelap Island, in the southern part. Analysis of variance gave an F value of 23.98 (significant at 1 per cent level), indicating that the difference in cesium-137 values between these two islands is statistically significant. At Eniaetok Island, which lies about half way between Rongelap Island and Kabelle Island, only three samples were obtained, two in March 1958, and one in August 1958. In the former collection the levels were higher than at Kabelle while in the latter collection the level was lower than at Kabelle for the corresponding dates. This apparent inconsistency is probably a result of individual vari- ation. At Utirik Atoll, which lies some 200 miles to the east (Fig. 1), the levels were about one-tenth of the lowest levels at Rongelap. The gamma dose rates give an indication of the relative levels of radioactive contamination of the different islands. The average gamma dose rates measured three feet above ground in March 1959 lands were, Rongelap 031, Eniaetok .051, at these is- Kabelle .069 and Utirik . 025, expressed as milliroentgens per hour. Determinations of other radionuclides in Birgus muscle indicate that over 90 per cent of the radioactivity is from cesium-137. wd ae en